Incontinence treatment device

ABSTRACT

A device and method for treatment of urinary stress incontinence. At least one electrode is implanted in a pelvic muscle of a patient. A control unit receives signals indicative of abdominal stress in the patient and responsive thereto applies an electrical waveform to the electrode which stimulates the muscle to contract, so as to inhibit involuntary urine flow through the patient&#39;s urethra due to the stress.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/167,244, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to medical electronic devices,and specifically to implantable electrical muscle stimulators.

BACKGROUND OF THE INVENTION

Urinary stress incontinence affects millions of people, causingdiscomfort and embarrassment, sometimes the point of social isolation.Stress incontinence results from weakness or inability of pelvic musclesto hold back urinary flow from the bladder when abdominal pressureincreases due to everyday events such as coughing, laughing or mildphysical exertion. Muscles involved in controlling the urinary flowinclude primarily the urethral sphincter and the levator ani, with thecooperation of fibromuscular extensions along the urethra and othermuscles in the general region of the pelvic diaphragm. In the UnitedStates, it is estimated that 10-13 million patients seek medical carefor incontinence each year, of whom about 35% suffer from stress-typeincontinence.

Stress incontinence is typically associated with either or both of thefollowing anatomical conditions:

Urethral hypermobility—Weakness of or injury to pelvic floor musclescauses the bladder to descend during abdominal straining or pressure,allowing urine to leak out of the bladder. This is the more commonsource of stress incontinence.

Intrinsic sphincter deficiency—In this condition, the urethralmusculature is unable to completely close the urethra or keep it closedduring stress.

A large variety of products and treatment methods are available forpersonal and medical care of incontinence. Most patents suffering frommild to moderate incontinence use diapers or disposable absorbent pads.These products are not sufficiently absorbent to be effective in severecases. They are uncomfortable to wear, and cause skin irritation, aswell as unpleasant odors. Other non-surgical products for controllingincontinence include urethral inserts (or plugs) and externally-wornadhesive patches. Drugs are also used in some cases.

Various surgical procedures have been developed for bladder necksuspension, primarily to control urethral hypermobility by elevating thebladder neck and urethra. These procedures typically use bone anchorsand sutures or slings to support the bladder neck. The success rates forbladder neck suspension surgery in controlling urinary leakage aretypically in the 60-80% range, depending on the patient's condition, thesurgeon and the procedure that is used. The disadvantages of surgery areits high cost, need for hospitalization and long recovery period, andhigh frequency of complications.

For serious cases of intrinsic sphincter deficiency, artificial urinarysphincters have been developed. For example, the AMS 800 urinarysphincter, produced by American Medical Systems Inc., of Minnetonka,Minn., includes a periurethral inflatable cuff, used to overcome urinaryincontinence when the function of the natural sphincter is impaired. Thecuff is coupled to a manually-operated pump and a pressure regulatorchamber, which are implanted in a patient's body together with the cuff.The cuff is maintained at a constant pressure of 60-80 cm of water,which is generally higher than the bladder pressure. To urinate, thepatient releases the pressure in the cuff by pressing on the implantedpump, which pumps the fluid out of the cuff to the chamber. Aspects ofthis system are described in U.S. Pat. No. 4,222,377, whose disclosureis incorporated herein by reference.

This artificial sphincter has several shortcomings, however. Theconstant concentric pressure that the peripheral cuff exerts on theurethra results in impaired blood supply to tissue in the area, leadingto tissue atrophy, urethral erosion and infection. Furthermore, theconstant pressure in the cuff is not always sufficient to overcometransient increases in bladder pressure that may result from straining,coughing, laughing or contraction of the detrusor muscle, for example.In such cases, urine leakage may result.

U.S. Pat. Nos. 4,571,749 and 4,731,083, whose disclosures areincorporated herein by reference, describe an artificial sphincterdevice whose pressure can vary in response to changes in abdominal orintravesical (bladder) pressure. The device includes a periurethral cuffwith subdermal pump and pressure regulator, with the addition of ahydraulic pressure sensor. This system is complicated, however, andrequires manual manipulation of the subdermal pump and cuff control.

Medtronic Neurological, of Columbia Heights, Minn., produces a deviceknown as Interstim for treatment of urge incontinence, which is adifferent disorder from stress incontinence. In urge incontinence, asudden, urgent need to pass urine causes involuntary urination, beforethe patient can get to a toilet. The condition may be caused by damageto nerve pathways from the brain to the bladder or by psychosomaticfactors, leading to involuntary bladder contraction. Interstim uses animplantable pulse generator, which is surgically implanted in the lowerabdomen and wired to nerves near the sacrum (the bone at the base of thespine) in a major surgical procedure under general anesthesia.Electrical impulses are then transmitted continuously to a sacral nervethat controls urinary voiding. The continuous electrical stimulation ofthe nerve has been found to reduce or eliminate urge incontinence insome patients.

Exercise and behavioral training are also effective in some cases inrehabilitating pelvic muscles and thus reducing or resolvingincontinence. Patients are taught to perform Kegel exercises tostrengthen their pelvic muscles, which may be combined with electricalstimulation of the pelvic floor. Electromyographic biofeedback may alsobe provided to give the patients an indication as to the effectivenessof their muscular exertions. Retraining muscles is not possible or fullyeffective for most patients, however, particularly when there may beneurological damage or other pathologies involved.

U.S. Pat. No. 3,628,538, whose disclosure is incorporated herein byreference, describes apparatus for stimulating a muscle, using anelectromyogram (EMG) signal sensed in the muscle. If the signal isgreater than a predetermined threshold value, a stimulator circuitapplies a voltage to electrodes adjacent to the muscle. The apparatus issaid to be particularly useful in overcoming incontinence.

Various types of electrodes have been proposed for applying electricalstimulation to pelvic muscles so as to prevent unwanted urine flowthrough the urethra. For example, U.S. Pat. No. 5,562,717 describeselectrodes that are placed on the body surface, typically in the areasof the perineum and the sacrum, and are electrically actuated to controlincontinence. U.S. Pat. No. 4,785,828 describes a vaginal plug havingelectrodes on an outer surface thereof. A pulse generator in the plugapplies electrical pulses to the electrodes so as to constrict thepelvic muscles and prevent urine flow. U.S. Pat. No. 4,153,059 describesan intra-anal electrode, to which repetitive electrical pulses areapplied in order to control urinary incontinence. U.S. Pat. No.4,106,511 similarly describes an electrical stimulator in the form of aplug for insertion into the vagina or the anus. U.S. Pat. No. 3,666,613describes a pessary ring having two electrodes thereon, which areenergized to control incontinence. The disclosures of all of theabove-mentioned patents are incorporated herein by reference.

U.S. Pat. No. 4,580,578, whose disclosure is also incorporated herein byreference, describes a device for stimulating the sphincter musclescontrolling the bladder. A supporting body is fitted into the patient'svulva between the labia, so that two electrodes attached to thesupporting body contact the epidermal surface on either side of theexternal urethral orifice. Electrical impulses are applied to theelectrodes to stimulate the region of the sphincter.

SUMMARY OF THE INVENTION

It is an object of sore aspects of the present invention to provide animproved device and method of treatment for incontinence, particularlyurinary stress incontinence.

It is a further object of some aspects of the present invention toprovide a device and method for enhancing function of muscles,particularly those associated with urine control.

In preferred embodiments of the present invention, an implantable devicefor treatment of urinary stress incontinence comprises a control unitand one or more electrodes coupled to the control unit. The electrode orelectrodes are preferably implanted in the genital region of a patientso as to contact one or more of the muscles that are used in regulatingurine flow from the bladder. The control unit is preferably implantedunder the skin of the abdomen or genital region. Motion of or pressureon or in the area of the bladder generates an electromyographic (EMG)signal in the muscles, which is sensed by the one or more electrodes andanalyzed by the control unit. Alternatively or additionally,non-electromyographic signals are received and analyzed by the controlunit, as described hereinbelow. When the control unit determines thatthe signals are indicative of a condition, such as an increase inabdominal or intravesical pressure, that is likely to cause involuntaryurine flow from the bladder, it applies an electrical waveform to theelectrode or electrodes, stimulating the contacted muscle to contractand thus to inhibit the urine flow.

In some preferred embodiments of the present invention, the device alsoincludes one or more other physiological sensors, which generate signalsresponsive to motion or to intravesical or abdominal pressure, or tourine volume in the bladder. These signals are thus indicative ofpossible incontinence that may occur due to coughing, laughing, or otherstrain or motion of the abdominal muscles. On the other hand, when theurine volume in the bladder is low, there will be no urine flow evenwhen the abdominal pressure does increase. The control unit processesthe signals from the other sensors and uses them to determine when theelectrical stimulation should be applied to the muscles.

Preferably, the control unit comprises a processor, which is programmedto distinguish between signals indicative of possible incontinence andother signals that do not warrant stimulation of the muscles. Inparticular, the processor is preferably programmed to recognize signalpatterns indicative of normal voiding, and does not stimulate themuscles when such patterns occur, so that the patient can pass urinenormally. Preferably, the processor analyzes both long-term andshort-term variations in the signals, as well as rakes and patterns ofchange in the signals. Most preferably, in response to the analysis, theprocessor: (a) makes an assessment of the patient's physiologicalcondition, such as of the patient's bladder fill level, (b) responsiveto the assessment, adjusts a time-varying threshold level associatedwith an aspect of the EMG signal (e.g., magnitude and/or rate) thatvaries over time, and (c) applies the stimulation only when a transientvariation in the aspect of the EMG signal exceeds the threshold.

Further preferably, in order to reduce consumption of electrical power,the control unit comprises a low-power, low-speed processor, whichmonitors the EMG signals continuously, and a high-speed processor, whichturns on only when the low-speed processor detects an increase in EMGactivity. The high-speed processor performs an accurate analysis of thesignals to determine whether stimulation is actually warranted. Theinventor have found that the signals must generally be analyzed at asample rate greater than 1000 Hz in order to accurately forecast whetheror not involuntary urine loss is about to occur.

Preferably, the electrodes are implanted (unlike electrical musclestimulators known in the art) and generally apply electrical stimulationdirectly into the muscle only when contraction is actually required,preferably as indicated by intrinsic physiological signals. At othertimes, stimulation is not applied, and the muscles are allowed to relax.Implantation of the device provides reliable, typically long-termcontrol or muscle function, and relieves incontinence in a manner thatis unobtrusive and minimizes inconvenience and discomfort of thepatient. The stimulation mimics the natural function of the muscles inmaintaining urinary continence. Repeated stimulation using theseembodiments of the present invention also tends to exercise andstrengthen the muscles, thus enhancing their inherent capability tocontrol urine flow. Direct stimulation of the muscles, in accordancewith the principles of these embodiments of the present invention, isbelieved to be effective against urine loss due to substantially allcommon types of stress incontinence.

Although preferred embodiments of the present invention are describedwith reference to treatment of urinary stress incontinence, it will beappreciated that the principles of the present invention may be appliedas well to treat other types of urinary incontinence, such as urgeincontinence, to fecal incontinence, and to treat and enhance thefunction of other muscles in the body. Alternatively or additionally,principles of the present invention may be applied to treatingconstipation or pathological retention of urine, typically bystimulating some muscles to contract (e.g., muscles of the colon), whilestimulating some parasympathetic nerves to induce relaxation of othermuscles (e.g., the muscles of the anus). These applications of theinvention may be particularly useful following spinal cord injury.

There is therefore provided, in accordance with a preferred embodimentof the present invention, a device for treatment of urinary stressincontinence, including:

at least one electrode, which is implanted in a pelvic muscle of apatient; and

control unit, which receives signals indicative of abdominal stress inthe patient and responsive thereto applies an electrical waveform to theelectrode which stimulates the muscle to contract, so as to inhibitinvoluntary urine flow through the patient's urethra due to the stress.

Preferably, the signals include electromyographic signals received fromthe at least one electrode, and the device includes a switch between theelectrode and an input of the control unit, which switch is opened whenthe electrical waveform is applied so as to prevent feedback from theelectrode to the input.

Preferably, the control unit includes a processor, which analyzes thesignals so as to determined when an involuntary urine flow is likely,whereupon the waveform is applied. Further preferably, the processordistinguishes between signals indicative of an involuntary urine flowand signals indicative of voluntary voiding by the patient. Preferably,the processor is programmable to vary one or more parameters associatedwith the application of the waveform, and the device includes a wirelessreceiver, which receives data for programming the processor from aprogramming unit outside the patient's body.

Preferably, the processor's analysis is performed on substantiallynon-rectified data. Further preferably, the processor analyzes thesignals using spectral analysis. Most preferably, the spectral analysisis performed by the processor on substantially non-rectified data.

Preferably, the at least one electrode includes a single unipolarelectrode or, alternatively or additionally, a pair of bipolarelectrodes. Further preferably, the at least one electrode includes aflexible intra-muscular electrode.

In a preferred embodiment, the device includes a physiological sensorcoupled to the patient's bladder, which sensor provides at least some ofthe signals to the control unit. Preferably, the sensor includes apressure sensor or, alternatively or additionally, an accelerationsensor.

Preferably, the at least one electrode and the control unit areimplanted in the body of the patient, and the control unit includes arechargeable power source. Most preferably, the power source isrecharged by inductive energy transfer, substantially without electricalcontact between the control unit and any object outside the patient'sbody.

Preferably, the pelvic muscle includes the levator ani muscle or,alternatively or additionally, the urethral sphincter muscle or anothermuscle adjacent to the urethral sphincter muscle.

There is further provided, in accordance with a preferred embodiment ofthe present invention, a device for treatment of urinary incontinence ina patient, including:

a sensor, which is coupled to generate a signal responsive to a filllevel of the patient's bladder; and

a control unit, which receives and analyzes the signal from the sensorso as to determine a fill level of the bladder and responsive theretoapplies stimulation to a pelvic muscle of the patient, so as to inhibitinvoluntary flow of urine through the patient's urethra when the filllevel of the bladder is above a threshold level.

Preferably, the control unit receives a further signal indicative ofabdominal stress and applies the stimulation to the pelvic muscleresponsive to the stress except when the fill level of the bladder isbelow the threshold level. In a preferred embodiment, the sensorincludes an electrode, which is plated in electrical contact with thepelvic muscle of the patient to receive an electromyogram signaltherefrom indicative of the stress and of the fill level.

Preferably, the device includes an electrode, which is placed inelectrical contact with the pelvic muscle of the patient, and thecontrol unit applies an electrical waveform to the electrode so as tostimulates the muscle to contract, thereby inhibiting the involuntaryflow of urine.

In another preferred embodiment, the sensor includes a pressure sensoror, alternatively or additionally, an ultrasound transducer.

There is moreover provided, in accordance with a preferred embodiment ofthe present invention, a device for treatment of urinary stressincontinence, including:

at least one electrode, which is placed in electrical contact with apelvic muscle of a patient; and

a control unit, which receives electromyogram signals from the electrodeindicative of abdominal stress in the patient, and which determines athreshold signal level that varies over time responsive to a conditionof the patient, and which, responsive to a transient increase in theelectromyogram signal above the threshold level, applies an electricalwaveform to the electrode which simulates the muscle to contract, so asto inhibit involuntary urine flow through the patient's urethra due tothe stress.

Preferably, the threshold signal level varies over time responsive totemporal variation of a mean value of the electromyogram signals.Additionally or alternatively, the threshold signal level increasesresponsive to time elapsed since the patient last passed urine orresponsive to an increase in a fill level of the patient's bladder.

There is additionally provided, in accordance with a preferredembodiment of the present invention, a device for treatment of urinarystress incontinence, including:

at least one electrode, which is placed in electrical contact with apelvic muscle of a patient; and

a control unit, which receives electromyogram signals from the electrodeand, responsive to a rate of change of the signals indicative of apossible involuntary urine flow, applies an electrical waveform to theelectrode which stimulates the muscle to contract, so as to inhibit theinvoluntary urine flow.

Preferably, when the rate of change is below a threshold rate, thecontrol unit withholds the waveform so as to allow voluntary voiding.

There is also provided, in accordance with a preferred embodiment of thepresent invention, a method for treatment of urinary stress incontinenceof a patient, including:

implanting an electrode in a pelvic muscle of the patient;

receiving a signal from the patient's body indicative of abdominalstress; and

responsive to the signal, applying an electrical waveform to theelectrode, which stimulates the muscle to contract so as to inhibitinvoluntary urine flow through the urethra due to the stress.

Preferably, applying the electrical waveform includes implanting anelectrode in the patient's body in electrical contact with the pelvicmuscle, most preferably with the levator ani muscle or, alternatively oradditionally, in contact with the urethral sphincter muscle or inproximity thereto.

Further preferably, applying the waveform includes applying a waveformto the electrode in a unipolar mode. Alternatively or additionally,implanting the electrode includes placing at least two electrodes inelectrical contact with the muscle, and applying the waveform includesapplying a waveform between the electrodes in a bipolar mode.

Preferably, receiving the signal includes receiving an electromyographicsignal.

In a preferred embodiment, receiving the signal includes receiving asignal indicative of pressure on the patient's bladder or, alternativelyor additionally, receiving a signal indicative of motion of thepatient's bladder.

Preferably, applying the waveform includes analyzing the signal todetermine when an involuntary urine flow is likely, and applying awaveform dependent on the determination, wherein analyzing the signalpreferably includes distinguishing between a signal indicating that theinvoluntary urine flow is likely and another signal indicative ofvoluntary voiding.

Preferably, analyzing the signal includes analyzing substantiallynon-rectified data. Further preferably, analyzing the signal includesperforming a spectral analysis. Most preferably, performing the spectralanalysis includes performing the spectral analysis on substantiallynon-rectified data.

In a preferred embodiment, applying the waveform includes varying aparameter of the waveform selected from a group including amplitude,frequency, duration, wave shape and duty cycle. Alternatively oradditionally, applying the waveform includes applying a pulse burst.

There is further provided, in accordance with a preferred embodiment ofthe present invention, a device for treatment of urinary stressincontinence, including:

at least one electrode, which is placed in electrical contact with apelvic muscle of a patient; and

a control unit, which receives signals indicative of impending urineflow, and distinguishes signals indicative of an involuntary urine flowfrom signals indicative of voluntary voiding by the patient, andresponsive thereto applies an electrical waveform to the electrode whichstimulates the muscle to contract, so as to inhibit involuntary urineflow.

Preferably, the control unit distinguishes between the signalsindicative of an involuntary urine flow and the signals indicative ofvoluntary voiding, substantially without application of an input to thecontrol unit from outside the patient's body.

There is still further provided, in accordance with a preferredembodiment of the present invention, a device for treatment of urinarystress incontinence, including:

at least one electrode, which is placed in electrical contact with apelvic muscle of a patient; and

a control unit, which receives at a sample rate substantially greaterthan 1000 Hz signals indicative of abdominal stress in the patient,analyzes the signals so as to determine when an involuntary urine flowis likely and responsive thereto applies an electrical waveform to theelectrode which stimulates the muscle to contract, so as to inhibitinvoluntary urine flow through the patient's urethra due to the stress.

There is moreover provided, in accordance with a preferred embodiment ofthe present invention, a device for treatment of urinary stressincontinence, including:

at least one electrode, which is placed in electrical contact with apelvic muscle of a patient;

a first processor, which receives signals indicative of abdominal stressin the patient and analyzes the signals substantially continuously at alow data analysis rate; and

a second processor, which, responsive to a determination by the firstprocessor that involuntary urine flow is likely to occur, is actuated bythe first processor to analyze the signals at a high data analysis rateand; responsive to the analysis at the high data rate, applies anelectrical waveform to the electrode which stimulates the muscle tocontract, so as to inhibit involuntary urine flow.

There is also provided, in accordance with a preferred embodiment of thepresent invention, a method for treatment of urinary stress incontinenceof a patient, including:

placing an electrode in electrical contact with a pelvic muscle of thepatient;

receiving a signal from the patient's body indicative of abdominalstress;

analyzing the received signal to distinguish between a signal indicatingthat involuntary urine flow is likely and another signal indicative ofvoluntary voiding; and

responsive to the analysis, applying an electrical waveform to theelectrode, which stimulates the muscle to contract so as to inhibitinvoluntary urine flow.

There is further provided, in accordance with a preferred embodiment ofthe present invention, a method for treatment of urinary stressincontinence of a patient, including:

placing an electrode in electrical contact with a pelvic muscle of thepatient;

receiving at a sample rate substantially greater than 1000 Hz signalsindicative of abdominal stress;

analyzing the signals so as to determine when an involuntary urine flowis likely; and

responsive to the analysis, applying an electrical waveform to theelectrode, which stimulates the muscle to contract so as to inhibitinvoluntary urine flow.

The present invention will be more fully understood from the followingdetailed description of the preferred embodiments thereof, takentogether with the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, pictorial view of an implantable musclestimulation device, in accordance with a preferred embodiment of thepresent invention;

FIG. 2 is a schematic, partly sectional illustration showingimplantation of the device of FIG. 1 in the. pelvis of a patient, inaccordance with a preferred embodiment of the present invention;

FIG. 3 is a schematic block diagram illustrating circuitry used in animplantable muscle stimulation device, in accordance with a preferredembodiment of the present invention;

FIG. 4 is a schematic block diagram illustrating circuitry used in animplantable muscle stimulation device, in accordance with anotherpreferred embodiment of the present invention;

FIG. 5 is a schematic block diagram illustrating signal processingcircuitry for analyzing electromyogram signals, in accordance with apreferred embodiment of the present invention; and

FIGS. 6 and 7 are graphs showing simulated and measured electromyogramsignals, representative of different aspects of use of an implantablemuscle stimulation device, in accordance with a preferred embodiment ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

I. Overview of Preferred Embodiments

A. General description of stimulator device

B. Sensing and control functions of the device

C. Signal processing

D. Power consumption control

II. Detailed Description of Figures

A. External elements of a stimulator device

B. Anatomical and surgical considerations

C. Signal processing

-   -   (i) hardware and algorithms    -   (ii) simulation of a typical EMG    -   (iii) experimentally measured EMG signals: distinguishing        incontinence from voluntary voiding

D. Muscle stimulation

E. Provision of power to the control unit

F. External communication with the control unit

G. Utilization of other sensors

H. Reduction of power consumption

I. Overview of Preferred Embodiments

A. General Description of Stimulator Device

Various aspects of the present invention are described in this section(I) and in greater detail in the following section (II). As describedwith reference to the preferred embodiment shown in FIG. 1, anelectronic muscle stimulator device is implanted in the genital regionof a patient and stimulates one or more of the muscles in the region, soas to control and treat urinary stress incontinence. Preferably, motionof or pressure on or in the area of the patient's urinary bladdergenerates an electromyographic (EMG) signal in the muscles, which issensed by one or more electrodes and is analyzed by a control unit ofthe device. Alternatively or additionally, non-electromyographic signalsare received and analyzed by the control unit. When the control unitdetermines that the signals are indicative of a condition, such as anincrease in abdominal or intravesical pressure, that is likely to causeinvoluntary urge flow from the bladder, it applies an electricalwaveform to the one or more electrodes, stimulating the contacted muscleto contract and thus to inhibit the urine flow.

B. Sensing and Control Functions of the Device

In addition to EMG sensing electrodes, the device preferably alsocomprises one or more other physiological sensors, described hereinbelowwith reference to FIGS. 2-4, which generate signals responsive tomotion, to intravesical or abdominal pressure, or to urine volume in thebladder. These signals are indicative of possible incontinence that mayoccur due to coughing, laughing, or other strain or motion of theabdominal muscles. Typically, when the urine volume in the bladder islow, there will be no urine flow even when the abdominal pressure doesincrease. As described with reference to a plurality of the figures, thecontrol unit preferably processes the signals from the other sensors anduses them to determine when the electrical stimulation should be appliedto the muscles.

C. Signal Processing

Preferably, the control unit comprises a processor, e.g., as describedwith reference to FIGS. 3 and 4, which is programmed to distinguishbetween signals indicative of possible incontinence and other signalsthat do not warrant stimulation of the muscles. In particular, theprocessor is preferably programmed to recognize signal patternsindicative of normal voiding, and does not stimulate the muscles whensuch patterns occur, so that the patient can pass urine normally.Detection of normal voiding is described in more detail with referenceto FIG. 7. Preferably, the processor analyzes both long-term andshort-term variations in the signals, as well as rates, spectralpatterns, and patterns of change in the signals. Most preferably, inresponse to the analysis, the processor sets a threshold of an aspect ofthe EMG signal that varies over time responsive to an assessment of thepatient's physiological condition, and applies the stimulation only whena transient variation in the aspect of the EMG signal exceeds thethreshold. Methods for modifying the threshold in real time aredescribed with reference to FIG. 6. In the context of the present patentapplication and in the claims, a “time-varying threshold” is to beunderstood as comprising substantially any appropriate time-varyingdetection parameters that a person skilled in the art, having read thedisclosure of the present patent application, would consider useful inapplying the principles of the present invention. By way of illustrationand not limitation, these time-varying detection parameters may includemagnitude, rate, or other aspects of the EMG signal, and quantitativeultrasound, pressure, or acceleration measurements, as described herein.

D. Power Consumption Control

As described with reference to FIG. 5, the control unit preferablycomprises a low-power, low-speed processor, which monitors the EMGsignals continuously, and a high-speed processor, which turns on onlywhen the low-speed processor detects an increase in EMG activity. Use ofthe two processors has been shown to significantly reduce consumption ofelectrical power. The high-speed processor performs an accurate analysisof the signals to determine whether stimulation is actually warranted.

II. Detailed Description of Figures

A. External Elements of a Stimulator Device

Reference is now made to FIG. 1, which is a schematic, pictorialillustration of an implantable electronic muscle stimulator device 20,in accordance with a preferred embodiment of the present invention.Device 20 is preferably implanted in the genital region of a patient, asdescribed further hereinbelow, for use in stimulating one or more of themuscles in the region, so as to control and treat urinary stressincontinence.

Device 20 comprises a control unit 22 and electrodes 27 and 29, mutuallycoupled by an electrical lead 24. The electrodes are preferably flexibleintramuscular-type wire electrodes, about 1-5 mm long and 50-100 micronsin diameter, thus designed to minimize patient discomfort. They aretypically formed in the shape of a spiral or hook, as is known in theart, so that they can be easily and permanently anchored in the muscle.The wire from which the electrodes are made comprises a suitableconductive material, preferably a biocompatible metal such as silver, aplatinum/iridium alloy (90/10) or a nickel/chromium alloy. Lead 24 ispreferably 5-10 cm long and has an insulating jacket 26 preferablycomprising nylon, polyurethane, Teflon or other flexible, biocompatibleinsulating material. An optional additional wire 28 inside jacket 26serves as an antenna for the purpose of wireless communications withdevice 20, as described further hereinbelow.

Control unit 22 contains circuitry, described further hereinbelow withreferences to FIGS. 3, 4 and 5, for receiving electrical signals fromand applying a waveform to electrodes 27 and 29 via lead 24. Thecircuitry is preferably contained in a case 25, made of stainless steelor other suitable biocompatible metal, and is preferably about 20 mm indiameter and 4 mm thick. For some applications, the stainless steel caseserves as a ground electrode for electrodes 27 and 29 when they aresensing or stimulating in a bipolar mode. Alternatively, the case may bemade of a plastic material which is coated with a layer of biocompatibleplastic, such as polymethyl methacrylate (PMMA) or silicone. Althoughtwo electrodes are shown attached to the control unit in FIG. 1, it ispossible to use only a single electrode or, alternatively, additionalelectrodes and/or other sensors may similarly be coupled to the controlunit, as described further hereinbelow.

B. Anatomical and Surgical Considerations

FIG. 2 is a schematic, partly sectional illustration showing thegenitourinary anatomy of a female patient 31 in whom device 20 isimplanted, in accordance with a preferred embodiment of the presentinvention. It will be appreciated that whereas preferred embodiments ofthe present invention are described with respect to female patients, theprinciples of the present invention can also be applied to malepatients, mutatis mutandis. Electrodes 27 and 29 (not shown) arepreferably inserted into a muscle 32, in a vicinity of urethra 34 andbladder 36. Most preferably, the electrodes are inserted into thepatient's levator ani muscle, which supports and reinforces theoperation of the urethral sphincter and can generally compensate forlost function of the sphincter in controlling urine flow from thebladder, such as may occur in cases of stress incontinence. Theelectrodes are preferably inserted through an incision made in the wallof vagina 42, and control unit 22 may likewise be implanted through thisincision. Alternatively, another suitable approach may be chosen forease of access and minimization of tissue trauma.

As noted hereinabove, the levator ani and sphincter cooperate withfibromuscular extensions along urethra 34 and with other muscles in thegeneral vicinity of the pelvic diaphragm. Thus, one or both of theelectrodes may, alternatively or additionally, be inserted into one ofthese other muscles, such as the puborectalis, pubococcygeus,bulboscongiosus or the urethral sphincter itself. The precise placementof the electrodes is not essential, particularly since electricalsignals tend to pass among the different muscles in the region. Thus,any placement of the electrode in or on one or more of the pelvicmuscles suitable for exercising urine control is considered to be withinthe scope of this embodiment of the present invention.

Control unit 22 is preferably implanted under the skin in thegenitopelvic region of patient 31. Most preferably, the control unit isimplanted inside the patient's labia minora 38 or in the labia majora40, near muscle 32. Alternatively, the control unit is not implanted inthe patient's body, but is instead maintained outside the body,connected by lead 24 to the electrodes. This configuration is convenientparticularly for an initial test period, during which the effectivenessof device 20 in treating a given patient is evaluated before permanentimplantation.

Optionally, a miniaturized ultrasound transducer 44 is implanted inproximity to bladder 36 and is coupled to control unit 22. Signals fromthe transducer are analyzed to estimate the urine volume within thebladder. When the bladder is empty, there is no need to actuateelectrodes 27 and 29, even when a transient increase in theelectromyogram (EMG) signal, as described hereinbelow, indicates anincrease in abdominal pressure. Alternatively or additional, the EMGsignal itself is analyzed to gain an indication of the urine volume inthe bladder, since when the bladder is full, the average EMG activitytypically increases.

C. Signal Processing

-   -   (i) Hardware and Algorithms

FIG. 3 is a schematic block diagram showing circuitry used in controlunit 22 to receive signals from and apply electrical waveforms toelectrode 27, in accordance with a preferred embodiment of the presentinvention. Although in this embodiment, device 20 is described asoperating in a unipolar mode, the principles described hereinbelow areapplicable to bipolar operation, as well, in which both electrodes 27and 29 are active.

When stress is applied to the abdomen of patient 31, electrode 27receives EMG signals from muscle 32. These signals are conveyed via aswitch 46, which is normally closed, to the input of an amplifier 48,preferably a low-noise operational amplifier. Amplified signals outputfrom amplifier 48 are digitized by an analog/digital (A/D) converter 50and conveyed to a central processing unit (CPU) 52, preferably amicroprocessor. Preferably, although not necessarily, the amplifiedsignals are not rectified prior to being digitized, to allow variousforms of analysis, for example, spectral analysis, to be performed onthe raw data, without the distortion imparted by rectification.

CPU 52 preferably analyzes these signals and/or signals from otherphysiological sensors, such as ultrasound, pressure, and accelerationsensors described hereinbelow, to determine whether they fit a patternindicating that incontinence, i.e., involuntary urine flow from bladder36, is likely to result from the stress. The pattern may correspond tocoughing, laughing, or other strain or motion of the abdominal muscles.The analysis preferably comprises a spectral analysis and an analysis ofEMG signal magnitude and rate. The CPU is programmed to distinguishbetween incontinence-related patterns and other signal patterns notassociated with incontinence, such as signals generated when patient 31wishes to pass urine voluntarily. Preferably, the CPU gathers long-termstatistical information regarding the EMG and analyzes the informationto “learn” common signal patterns that are characteristic of patient 31.The learned patterns are used in refining decision criteria used by theCPU in determining whether or not to apply waveforms to the electrodes.

-   -   (ii) Simulation of a Typical EMG

FIG. 6 is a graph that schematically illustrates results of a simulationexperiment, in accordance with a preferred embodiment of the presentinvention, including a simulated EMG signal 100 of a woman sufferingfrom stress incontinence. A variable, adaptive threshold level 102 asmarked on the graph. Over the course of several hours, as the woman'sbladder fill level increases, the average level of EMG signal 100increases accordingly. In this example, threshold level 102 is computedso as to increase as a function of the average EMG. Alternatively oradditionally, threshold level 102 and a plurality of other time-varyingdetection parameters are calculated as functions of other features ofthe EMG signal or of other aspects of the women's condition(particularly as measured by sensors 44, 76 and 78 (FIG. 4)), and areused separately or in combination in determining whether to applystimulation to inhibit involuntary urine flow. Adaptive threshold level102 enables five possible incidents of incontinence, marked byexcursions 104 of signal 100 over level 102, to be detected reliably,with a low false alarm rate. On the other hand, if a fixed thresholdlevel 106 is used, as is known in the art, a number of EMG excursions104 are missed, and the false alarm rate is high.

-   -   (iii) Experimentally Measured EMG Signals: Distinguishing        Incontinence from Voluntary Voiding

FIG. 7 includes graphs 110 and 112 that schematically illustrateexperimental measurements made before, during and after voluntaryvoiding of urine, in accordance with a preferred embodiment of thepresent invention. Graph 112 is a continuation in time of graph 110. Theupper trace in both graphs illustrates urine flow, wherein the beginningand end of voluntary flow are marked by arrows. The lower traceillustrates measured EMG signals.

In a period preceding voiding, an EMG signal 14 shows substantialhigh-frequency activity, which is generally indicative of a fullbladder. As illustrated by the graphs in the preceding figures,high-frequency spikes in signal 114 (of which none appear in FIG. 9)would be interpreted by CPU 52 as signs of imminent incontinence,leading to actuation of pulse generator 54. On the other hand, voluntaryvoiding is precedes by an EMG signal 116, in which there is a large butgradual increase in the signal level. Signal 116 is associated withvoluntary activation of the pelvic floor muscles for the purpose ofpassing urine from the bladder, as is a later signal 118 during voiding.Therefore, CPU 52 analyzes not only the level of the EMG signals, butalso a rate of change of the signals, in order to distinguish betweenvoluntary and involuntary contractions of the pelvic muscles. When therate of charge is characteristic of voluntary voiding, no stimulation isapplied by pulse generator 54.

D. Muscle Stimulation

When possible incontinence is detected in this manner, CPU 52 opensswitch 46 and commands a pulse generator 54 to apply a suitableelectrical waveform to electrode 27 so as to stimulate muscle 32 tocontract. Switch 46 is opened in order to avoid feedback of thestimulation waveform; to amplifier 48, and is closed again after thewaveform is terminated. In the embodiment shown in FIG. 3, the waveformis applied to the electrode in a unipolar node, wherein case 25 ofcontrol unit 22 serves as the return (ground) electrode. (This mode canbe used only when case 25 comprises a conductive material. When controlunit 22 has a plastic case, at least two electrodes are generallyneeded, in order to administer bipolar stimulation.) As muscle 32contracts, it closes off urethra 34, thus inhibiting the undesired urineflow. Preferably, the waveform is terminated and switch 46 is closedafter a predetermined period of time, typically about 5 sec, has passed.If possible incontinence is again detected at this point, the waveformis re-applied.

It will be appreciated that, depending on the particular application,one or more waveforms may be employed in the practice of variousembodiments of the present invention. For example, the waveform may beuniphasic or biphasic and may have a range of amplitudes, duty cyclesand/or frequencies. It has been found generally that pulse frequenciesin the range between 5 and 200 Hz are effective in engenderingcontraction of the levator ani and other pelvic muscles, but it may alsobe possible to use frequencies outside this range. In a preferredembodiment, the waveform comprises a bipolar square wave having thefollowing characteristics:

Current 30-100 mA,

Voltage 9-15 V,

Pulse width 0.1-2.0 ms, variable in increments of 0.1 ms, and

Pulse repetition rate 30-50 Hz.

Alternatively, the waveform may comprise a decaying square wave,sinusoid or sawtooth or have any other shape found to be suitable.Further alternatively or additionally, the waveform may comprise one ormore bursts of short pulses, each pulse preferably less than 1 ms induration. Generally, appropriate waveforms and parameters thereof aredetermined during the initial test period.

E. Provision of Power to the Control Unit

Power is supplied to the elements of control unit 22 by a battery 56,which may comprise a primary battery (non-rechargeable) and/or arechargeable battery. Alternatively, a super-capacitor, as is known inthe art, may be used to store and provide the electrical power. If arechargeable battery or super-capacitor is used, it is preferablyrecharged via an inductive coil 56 or antenna, which receives energy bymagnetic induction from an external magnetic field charging source (notshown) hold in proximity to the pelvis of patient 31. The magnetic fieldcauses a current to flow in coil 58, which is rectified by a rectifier60 and furnished to charge battery 56. Wire 28 may also be used for thispurpose.

Preferably, battery 56 comprises a standard battery, such as a lithiumbattery, having a nominal output of 3 volts. Most preferably, pulsegenerator 54 comprises a DC/DC converter, as is known in the art, and acapacitor, which is charged by the DC/DC converter to a constant,stepped-up voltage level regardless of the precise battery voltage,which may vary between 3.5 and 1.8 volts. The same DC/DC converter, oranother similar device, preferably supplies power to other circuitcomponents of control unit 22.

F. External Communication with the Control Unit

An inductive arrangement, using wire 28 coupled to CPU 52, is preferablyused to program the CPU, using an external programming device (notshown) with a suitable antenna. Alternatively, the programming devicegenerates a modulated magnetic field to communicate with a receiverinside case 25, which preferably senses the field using a Hall effecttransducer. Such programming may be used, for example, to set anamplitude or duration of the stimulation waveform applied by pulsegenerator 54, or to set a threshold level or other parameters, accordingto which the CPU distinguishes between electromyographic or othersignals that are indicative of impending incontinence and those that arenot (e.g., those that indicate voluntary voiding). Such programming maybe carried out by medical personnel or by the patient herself, who cansimilarly turn the implanted control unit on and off as desired bypassing a suitable magnet over the area of her pelvis.

Although the circuit blocks in control unit 22 are shown as discreteelements, some or all of these blocks are preferably embodied in acustom or semi-custom integrated circuit device, as is known in the art.

G. Utilization of Other Sensors

FIG. 4 is a schematic block diagram illustrating a muscle stimulatordevice 70, in accordance with an alternative embodiment of the presentinvention. Device 70 is substantially similar to device 20, except forfeatures described hereinbelow. Device 70 comprises a control unit 74,which is coupled to electrodes 27 and 29. Electrode 29 also serves asthe sensing electrode, furnishing electromyographic signals via switch46 to amplifier 48, as described hereinabove. Alternatively, electrodes27 and 29 may be coupled as differential inputs to amplifier 49. Pulsegenerator 54 applies the stimulation waveforms between electrodes 21 and29 in a bipolar mode.

In addition to or instead of the electromyographic signals received fromelectrode 29, CPU 52 preferably receives additional signals from otherphysiological sensors, such as ultrasound transducer 44 (shown in FIG.2), a pressure sensor 76 and/or an acceleration sensor 78, or othertypes of strain and motion measurement devices, as are known in the art.Pressure sensor 76 is preferably implanted on or in bladder 36, so as todetect increases in abdominal or intravesical pressure that may lead toinvoluntary urine loss. Similarly, acceleration sensor 78 is preferablyimplanted so as to detect bladder motion associated with hypermobility,which is similarly associated with urine loss. The additional signalsfrom these sensors are preferably analyzed by the CPU together with theelectromyographic signals in order to improve the accuracy andreliability of detection of impending stress incontinence.

An impedance sensor 79 is used to measure the tissue impedance betweenleads 27 and 29, using physiological impedance measurement techniquesknown in the art. During long-term use of device 70 (or other suchdevices), fibrosis in the area of the implanted electrodes tends tocause the impedance to increase, so that the stimulating current for agiven applied voltage decreases. The impedance measured by sensor 79 isused as a feedback signal instructing CPU 52 to increase the voltage, sothat a generally constant level of simulation current is maintained.

H. Reduction of Power Consumption

FIG. 5 is a schematic block diagram showing details of signal processingcircuitry 80 for use in device 20 or 70, in accordance with a preferredembodiment of the present invention. In order to detect impendingincontinence with adequate reliability, A/D converter 50 must typicallysample the EMG signals from the electrodes at 1000-5000 Hz, and CPU 52must perform a detailed analysis of the sample stream. Systems forincontinence control known in the art, operating at sample rates below1000 Hz, cannot adequately distinguish between signals that may beindicative of incontinence and those that are not. For the purpose ofsuch high-rate sampling, CPU 52 preferably comprises a low-power,software-programmable processor. If A/D converter 50 and CPU 52 were tooperate continuously, however, battery 56 would rapidly run down.Therefore, circuitry 80 comprises a low-power, low-resolution A/Dconverter 84 and hard-coded processing logic 86, which operatecontinuously at a low sampling rate, preferably at about 100-200 Hz.Input from amplifier 48 to A/D converter 84 is preferably rectified by arectifier 82.

In operation, A/D converter 50 and CPU 52 are normally maintained in astandby state, in which their power consumption is negligible. Whenlogic 86, operating at the low sampling rate, detects EMG signals thatmay be a precursor to incontinence, it signals A/D converter 50 to beginsampling at the high rate. In order not to lose significant data fromthe brief period before A/D converter 50 and CPU 52 turn on, signalsfrom A/D converter 84 are preferably stored in a cyclic (or first-infirst-out) queue 88, such as a delay line. The entire sequence of signaldetection and processing is estimated to take between 5 and 20 is, up tothe point at which CPU 52 reaches a decision as to whether or not toactuate pulse generator 54. Pulse generation takes between 1 and 20 ms,with the result that contraction of the pelvic muscles begins within15-50 ms of the onset of increased EMG activity indicating impendingurine loss. Thus, urethra 34 is substantially closed off before anysignificant amount of urine can leak out.

As shown in FIG. 5, EMG inputs from electrodes 27 and 29 are preferablyamplified before processing in a dual-differential configuration.Electrode 27 and 29 are coupled to respective differential preamplifiers87 and 89. The outputs of the preamplifiers are differentially amplifiedby amplifier 48. This configuration, which affords enhanced sensitivityand reduced noise in device 70, is shown in FIG. 4.

Although preferred embodiments of the present invention are describedhereinabove with reference to treatment of urinary stress incontinence,it will be appreciated that the principles of the present invention maybe applied as well to treat other types of incontinence, such as urgeincontinence, and to treat and enhance the function of other muscles inthe body. It will be understood that the preferred embodiments describedabove are cited by way of example, and the full scope of the inventionis limited only by the claims.

1. A device for treatment of urinary stress incontinence, comprising: atleast one electrode, which is adapted to be implanted in a pelvic muscleof a patient; and a control unit, which receives signals indicative ofabdominal stress in the patient and responsive thereto applies anelectrical waveform to the electrode which stimulates the muscle tocontract, so as to inhibit involuntary urine flow through the patient'surethra due to the stress.